For a long time now I've recommended sh404SEF for most Joomla sites. Recently however, theres been a long post on the SEO Club Forum with users saying how much they like Artio SEF. Some reasons they gave:

• In Artio SEF you can search and filter SEF Urls in main ways such as by component which is awesome. In sh404sef, you can search...that's it.
• In Artio SEF you can edit an existing SEF Urls, in 404, you can edit the text, but not the link itself.
• Artio SEF doesn't have to have a specific plugin to at least attempt an SEF url for a component. If you have a link to an unsupported gallery component and your link is called "Gallery", JoomSEF will at least call that link /gallery.htm

The two components are built on the same code base so there are a lot of similarities. Today's open question is:

"Which do you prefer using ... Artio SEF or sh404SEF?"